The design of memory subsystems has become more complex as the need for higher speeds and Dynamic Random Access Memory (DRAM) densities continue to increase with an on-going requirement for smaller memory module form factors. Small memory module form factors such as Small Outline Dual In-Line Memory Modules (SO-DIMMs), Mini-Dual In-Line Memory Modules (Mini-DIMMs), and Very Low Profile (VLP) Dual In-Line Memory Modules (DIMMs) generally use specialized DRAM packaging technologies to achieve high density solutions.
As the complexity and level of integration increases, the number of devices and consequently the number of pins of an integrated circuit package that need to be connected to a circuit board becomes larger and larger. Ball Grid Array (BGA) is a well-known packaging technique that is used to permanently mount devices, such as microprocessors, to a circuit board. A BGA can provide more interconnection pins than can be put on a dual in-line or flat package as solder balls are located on the underside for surface mounting. To place the additional devices on the circuit board, typical BGA stacking techniques are used. However, typical BGA stacking techniques require an interposer printed circuit board (PCB) to join upper and lower memory devices electrically or mechanically together into a single standalone stacked component.
Consequently, devices and packaging methods are needed that minimize interposer size, and can mount an upper BGA chip over a lower BGA chip in an efficient process. Furthermore, compact interposers that permit a greater density of devices to be placed in a limited space are needed.